1. Field of the Invention
This invention generally relates to wireless communications, and, more specifically, to wireless communications networks that employ repeaters.
2. Related Art
It is often useful to extend the range of a communications network by adding repeaters. Many repeaters process signals by simply obtaining an input from a “donor” source, amplifying it, and then transmitting it at a “server” antenna. In some cases the repeater may modify the repeated signal, for example encapsulating packet data to be repeated within packets composed by the repeater. In many other situations, however, it may be useful for the repeater to be “transparent,” that is to provide the same signal from the repeater server antenna as is presented to the repeater donor antenna, so that network processing may often proceed without particular regard to the repeaters.
Repeaters may be utilized in a number of geometric configurations. FIG. 1 illustrates a repeater obtaining a signal from a donor antenna 102 disposed on top of a building 104. The donor antenna 102 may be configured to preferentially receive signals from a selected base station transmitter. For example, a moderately directional Yagi antenna aligned with a sector c transmitter of a base station BS1 106 preferentially receives signals transmitted from sector c of BS1 106. The base station BS1 106 is shown in a typical configuration for cellular telephone base stations, having three sectors identified as a-c. Each sector may be provided with a distinct RF transmission signal.
The donor antenna 102 is coupled, for example via an amplifier 108, to one or more server units 110. A server unit 110 may, for example, be provided on each floor of the building 104 to facilitate reception by receivers, such as MS-2 112, whose reception might otherwise be impaired because of being located within the building. The forward path from a base station to a receiver is illustrated in FIG. 1. Reverse paths from a receiver, such as MS-2 112, to a base station, such as BS1 106, are typically provided in a complementary manner, but are not shown or described extensively.
FIG. 2 illustrates a repeater configuration that may be used, for example, to extend the geographical coverage range of a cellular system. Supported at a location 202 that may be on a tower, high building or other relatively unobstructed site, the repeater 212 includes a donor antenna 204, an amplifier 206, and a server antenna 208. The donor antenna 204 is shown as a parabolic antenna aligned to a primary base station 210, but may also be a less directional antenna. The server antenna 208 generally broadcasts the signal over a relatively wide area, with coverage that may be similar or even broader than the coverage of the transmission from an ordinary base station sector.
FIG. 3 illustrates a repeater configuration that is frequently used for server antennas, such as server antenna 302, that are far removed from a primary signal source, such as a base station 304. A donor pickup device may be located within the base station 304. A signal may be provided to the pickup device 306 in many possible ways, some of which are indicated by broken lines. For example, the signal may be provided from a coupler 308 in a transmission line to a final RF amplifier 310. Alternatively, the signal may be provided from a coupler 312 subsequent to the amplifier 310, or it may be picked up by an antenna 314 that is closely coupled to a transmission antenna 316 of the base station. The signal obtained by the donor pickup 306 is then conveyed via a repeater link 318. The repeater link 318 may include extensive RF transmission lines and amplifiers to convey the signal a substantial distance to a final repeater amplifier 320 prior to the server antenna 302.
However, the repeater link 318 need not maintain the signal in the same form in which it is received from the base station 304. For example, the repeater link 318 may convert the signal received from the donor pickup 306 to an intermediate form having a different modulation or signaling scheme, so that the signal can be transferred via a special repeater link mechanism. Such repeater link mechanism may include fiber optics, or microwave relay stations, or any other suitable mechanism. The intermediate form may, for example, include encapsulating the information in the received signal within a frame structure uniquely employed by the special repeater link mechanism. Before presentation to the final repeater amplifier 320 and transmission from the server antenna 302, the signal is typically converted back into substantially the same form of modulation and signaling scheme it would have had if transmitted directly from the base station antenna 316. Many repeater configurations are variations upon those illustrated in FIGS. 1-3, and there are other geometries as well.
“Transparency” is a design goal for many repeaters, so that they may be employed in a system without requiring special accommodation. For many purposes, a system need not even take note as to whether or not a repeater is included in a transmission path. However, as set forth more particularly in the detailed description below, in some instances there is a need to know that a signal has traveled via a repeater, even if the repeater has been designed to be transparent to the system.